1. Field of the Invention
The present invention concerns organopolysiloxane compositions which are stable in storage in the absence of humidity and harden into elastomers at ambient temperatures in the presence of humidity. More particularly, the present invention relates to organopolysiloxane compositions comprised of a mixture of essentially linear hydroxyl polysiloxanes; fillers; cross-linking agents chosen from silanes having bonded to the silicon atom hydrolyzable groups either of the hydrocarbonoyloxy type of the formula R.sup.1 COO-- (also designated by the term acyloxy), in which the symbol R.sup.1 represents a hydrocarbon radical, or of the ketoniminoxy type of the formula R.sub.2.sup.2 C.dbd.NO--, in which the symbols R.sup.2, being either the same or different, represent an alkyl radical; and, hardening catalysts selected from among the organic derivatives of titanium or zirconium.
these organopolysiloxane compositions are designated single component in contrast to two-component organopolysiloxane compositions which also harden at ambient temperatures into elastomers, but are not stable in storage and must therefore be handled in two separate packages.
2. Description of the Prior Art
Single component organopolysiloxane compositions are known to the prior art. They are disclosed in numerous references and used in fields of application as varied as automobiles, electronics, the construction industry, and medicine. The catalysts used in the composition formulations generally are metallic salts of carboxylic acids, the metal of which may be lead, tin, nickel, cobalt, iron, cadmium, chromium, zinc, or manganese. The preferred metal is tin and the catalysts used are nearly always organic tin salts of carboxylic acids, such as dibutyl-tin diacetate or dilaurate. The choice is based on the ability of these organic tin salts to better accelerate the hardening of the compositions into elastomers.
Known single component compositions prepared with cross-linking agents consisting of silanes having hydrolyzable hydrocarbonoyloxy groups of the formula R.sup.1 COO--, with R.sup.1 representing a hydrocarbon radical and catalysts consisting of organic tin salts of carboxylic acids, are disclosed, for example, in U.S. Pat. Nos. 3,077,456, 3,382,205, 3,701,753, 3,957,714, 4,115,356 and 4,273,698; and FR No. 2,429,811 and FR No. 2,459,820. Other known single component compositions prepared from cross-linking agents consisting of silanes with hydrolyzable ketoniminoxy groups of the formula R.sup.2 C.dbd.NO--, with R.sup.2 representing an alkyl radical, and the same organic tin salts of carboxylic acids are disclosed, in particular, in U.S. Pat. Nos. 3,678,003 and 3,986,999; and, FR No. 2,415,132 and FR No. 2,421,195. Sometimes the organic tin salts of carboxylic acids are not used as such, but are used in the form of their reaction products with titanium esters, e.g., compare U.S. Pat. No. 3,409,753.
It is known that organic tin salts have the disadvantage of being toxic. For this reason, they cannot be introduced in single component compositions which are intended, after being hardened to elastomers, to be in contact with food products, pharmaceutical products or even prostheses. Furthermore, with the use of single component compositions constantly increasing, and in particular in the industrial applications of grouting, the embedding of electric and electronic equipment and the adhesive bonding of pieces of any kind, the degradation over time of the elastomers resulting from these compositions to thereby release tin salts will clearly contribute to the pollution of the environment.
There are additional families of catalysts that may be used in single component organopolysiloxane compositions, such as the family of organic derivatives of titanium. The use of titanium compounds is well known in compositions using only silanes containing hydrolyzable groups of the hydrocarbonoxy type, and more specifically alkoxy groups, as cross-linking agents. See, for example U.S. Pat. Nos. 3,334,067, 4,100,129, 4,102,852 and 4,273,698. These titanium catalysts are thus reserved for organopolysiloxane compositions with cross-linking agents containing so-called neutral alkyl groups, while for the so-called acid cross-linking agents carrying hydrocarbonoyloxy groups, tin salts are recommended. U.S. Pat. No. 4,273,698, for example, illustrates this different use well. Therein it is recommended, e.g., at column 1, lines 45-50 and column 7, lines 1 to 6 and 24 to 25, to use catalysts consisting of tin salts of carboxylic acids with cross-linking agents chosen from among silanes containing hydrocarbonoyloxy groups, and catalysts consisting of titanium chelates with cross-linking agents chosen from among silanes carrying alkoxy groups.
Certainly, one finds in the chemical literature indications suggesting compositions formulated by the mixture of hydroxyl organopolysiloxanes or containing hydrolyzable groups incorporating acyloxy (and more specifically acetoxy) groups, silanes, containing the same hydrolyzable groups and organic derivatives of titanium. Such compositions, however, are not exemplified and it is difficult to derive from the descriptions a clear illustration of the combinations consisting of silanes containing acyloxy or ketoniminoxy groups and organic titanium derivatives.
Compare, Belgian Pat. No. 744,184 wherein an interpretation of the broadest general formula described provides the possibility of a combination of an organotriacetoxysilane with a titanium chelate, the organotriacetoxysilane being introduced in a proportion of 0.1 to 20 parts and the titanium chelate in a proportion of 0.1 to 30 parts per 100 parts of a .alpha.,.omega.-dihydroxydiorganopolysiloxane.
In using organic zirconium derivatives as hardening catalysts, it is known to introduce in single component organopolysiloxane compositions zirconium salts of carboxylic acids. However, this introduction does not make it possible by itself to obtain a significant acceleration of the time to harden the compositions into elastomers. To obtain shorter durations, it is necessary to add an organic tin salt of a carboxylic acid, such as dibutyl-tin dilurate or dimethyl-tin neodecanoate. Compare, Belgian Pat. No. 877 845.
In view of the foregoing, the need arose to find a nontoxic, non-polluting catalytic system effective in small quantities, which exhibits an improved catalytic activity and permits one to obtain shorter elastomer cross-linking times for organopolysiloxane elastomers which have satisfactory mechanical properties. The present invention achieves this objective.